Several types of spacers for flat panel displays, such as field emission displays, are known in the art. A field emission display includes an envelope structure having an evacuated interspace region between two display plates. Electrons travel across the interspace from a cathode plate (also known as a cathode or a back plate), upon which electron emitting structures, such as Spindt tip or carbon nanotubes, are fabricated, on an anode plate (also known as an anode or face plate), which includes deposits of light emitting materials, or “phosphors”. Typically, the pressure within the evacuated interspace region between the cathode and anode is on the order of 10−6 Torr.
The cathode and anode plates are thin in order to provide low display weight. If the display area is small, such as in a 1 inch diagonal display, and a typical sheet of glass having a thickness of 0.04 inch is utilized for the plates, the display will not collapse or bow significantly. However, if a larger display area is desired, the thin plates are not sufficient to withstand the pressure differential in order to prevent collapse of bowing upon evacuation of the interspace region. For example, a screen having a 30 inch diagonal will have several tons of atmospheric pressure exerted upon it. As a result of this tremendous pressure, spacers play an essential role in large area, light weight displays. Spacers are structures placed between the anode and cathode plates for keeping them a constant distance apart. The spacers, in conjunction with the thin, light weight plates, counteract the atmospheric pressure, allowing the display area to be increased with little or no increase in plate thickness.
Several schemes have been proposed for providing spacers. Some of these schemes include the affixing of spacer (structural members) to the inner surface of one of the display plates. In one such prior art scheme, glass rods are affixed to one of the display plates by applying devitrifying solder glass frit to one end of the rod or post and bonding the frit to the inner surface of one of the display plates. This method includes problems such as bond brittleness, particulate contamination, smearing onto pixels, non-uniformity of the spacer height of the fritted spacer due to initial height variations in the original spacer and non-perpendicularity due to displacement due to cooling of the frit. Other proposed schemes for bonding spacers onto the display plate include the use of organic glue. However, organic glues are burned off before the package is sealed and differential pressure applied, thereby predisposing the spacers to being loosened or misplaced within the envelope of the display.
Another known method uses thermocompression bonding to smash one layer of metal into another layer of metal. The bond that is created is strong enough to permit handling and sealing of the device components. An anode electrode is coated with a patterned chrome oxide black matrix. A one micrometer thick aluminum layer is deposited and patterned on the chrome oxide layer to provide the bonding surface. Without this layer, the spacers do not bond. Before bonding, another aluminum layer, approximately 70 nanometers thick, is deposited over the first aluminum layer and the phosphor. This layer lies between the thick aluminum bonding surface and the ball-bumps on the spacer; however, since it is thin and perforated, it does not substantially alter the bonding requirements. These films mentioned above are deposited by vacuum deposition techniques, and the thick aluminum layer must be processed photolithography and etch tools.
The known art mentioned above was based on a CRT-like process for making the anodes. Recently, it has become apparent that the fabrication of the anodes can be done more cheaply for large area displays using plasma-display technologies, wherein a black matrix is deposited with screen printing, just like the phosphors. Screen printing eliminates the need to pattern thin films such as Chromium oxide and aluminum, and therefore eliminates the need for capital equipment and processes for vacuum deposition, photoresist coating, photoresist developing, and etching.
However, the spacers do not bond to the black surround screen-printed materials, such as Ruthenium oxide, and other known fabrication alternatives are expensive and not industry process compliant.
Accordingly, it is desirable to provide a spacer bonding technology that works with less expensive thick film techniques currently being applied in the plasma display industry. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description of the invention and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.